The present invention relates to a structure for filtering the exhaust gases from an internal-combustion engine, of the type comprising at least one filtering member comprising:                intake conduits for the gases to be filtered, into which respective gas intake openings emerge, at least some of the intake conduits emerging through openings for discharging respective residues provided downstream of the respective intake openings;        conduits for extracting filtered gases emerging into respective openings for extracting filtered gases, the extracting conduits being separated from the intake conduits by porous filtering walls.        
Structures of this type are used, in particular, in devices for controlling de-pollution of exhaust gases from motor vehicle diesel engines.
Filtering structures are known in which the filtering member comprises a set of adjacent conduits having parallel axes, separated by porous filtering walls. The conduits extend between an intake face and a discharge face. These conduits are closed at one or other of their ends to delimit gas intake conduits opening onto the intake face, and gas extracting conduits opening onto the discharge face.
The structures of the aforementioned type operate in accordance with a sequence of filtering phases and regeneration phases. During the filtering phases, the soot particles emitted by the engine are deposited on the walls of the inlet chambers. The loss in pressure through the filter increases gradually. Beyond a predetermined value of this pressure loss, a regeneration phase is carried out.
During the regeneration phase, the soot particles, basically composed of carbon, are burnt on the walls of the inlet chambers in order to restore the original properties of the structure.
However, the residues resulting from the burning of the soot accumulate in the base of the intake conduits. The initial loss in pressure through the structure therefore increases after each regeneration phase, and the distance covered between the regeneration phases decreases over the vehicle's life.
In order to overcome this problem, EP-A-1 408 207 discloses a structure of the aforementioned type in which slots for discharging residues are formed in the porous walls separating the intake conduits from the extracting conduits, in the vicinity of the discharge face.
At the start of a filtering phase, the soot preferably accumulates in the residue discharge slots and gradually blocks these slots to generate a counter-pressure in the intake chambers. During the regeneration phases, the residues from the burning of the soot flow into the extracting conduits through the slots and are discharged from the filtering member, then into the exhaust line.
A structure of this type is not entirely satisfactory. At the start of each filtering phase, a portion of the soot present in the intake gases passes through the filtering member without being filtered. Similarly, the combustion residues are discharged into the exhaust line during the regeneration phases. Then, even if the average effectiveness of the structure of the aforementioned type is improved, there remain phases for which this effectiveness is of less high quality.
A similar criticism can be made of the filtering structures of the aforementioned type described in documents EP-A-1 408 208 and EP-A-1 413 356.